The present invention relates to a leak sensing switch for detecting a leakage current and an insulating substrate having a leak sensing switch.
Power window apparatuses are used to automatically open and close the window glass panels of side doors or the like of vehicles. The window glass panels are elevated or lowered when a driver operates an up switch or a down switch of the power window apparatus. However, if the power window apparatus is immersed in water, a drive circuit for the drive motors of the power window apparatus tends to malfunction, failing to energize the drive motors. To solve the above problem, th drive circuit of the power window apparatus is provided with a leak sensing switch for detecting a leakage current. When the leak sensing switch detects a leakage current at the time the power window apparatus is immersed in water, the drive circuit becomes operational based on the detection of the leakage current.
FIG. 5 is a schematic plan view of a first conventional leak sensing switch 50. A pair of pattern wirings 52a, 52b extend parallel to each other on a circuit board 51, and first and second branch wirings 53a, 53b extending perpendicularly to the pattern wirings are disposed between the pattern wirings. Electrodes 54a, 54b produced by soldering are disposed respectivelyon the first and second branch wirings 53a, 53b. The electrodes 54a, 54b have a given length 11, and are spaced from each other by a predetermined gap g1. When the leak sensing switch 50 is immersed in water, a leakage current flows between the electrodes 54a, 54b, thus detecting the immersion in water.
FIG. 6 is schematic plan view of a second conventional leak sensing switch 55. A pair of pattern wirings 57a, 57b extend in series and is spaced from each other in a predetermined space on a circuit board 56, a C-shaped first electrode support 58a connected to the pattern wiring 57a and a circular second electrode support 58b connected to the pattern wiring 57b disposed between the pattern wirings 57a, 57b. The first electrode support 58a is spaced from the second electrode support 58b by a predetermined gap g2 and is disposed to surround the second electrode support 58b. Electrodes 59a, 59b produced by soldering are disposed respectively on the first and second electrode supports 58a, 58b. 
FIG. 7 is a schematic perspective view of a third conventional leak sensing switch 60. A base 62 of synthetic resin having insulating properties is disposed on a circuit board 61, and a pair of parallel electrode pins 63a, 63b are disposed on the base 62. The electrode pins 63a, 63b are electrically connected to a wiring pattern, not shown. The electrode pins 63a, 63b have a given length 13, and are spaced from each other bya predetermined gap g3.
When the difference between the temperature within the power window apparatus and the temperature outside the power window apparatus increases, moisture tends to be condensed in the power window apparatus, disadvantageously.
With the leak sensing switches 50, 55 shown in FIGS. 5 and 6, when water droplets are produced between the electrodes 54a, 54b and between the electrodes 59a, 59b due to dew condensation, a leakage current may flow between the electrodes 54a, 54b and between the electrodes 59a, 59b and may be detected even though the power window apparatus is not immersed in water.
With the leak sensing switch 60 shown in FIG. 7, however, since the electrode pins 63a, 63b are not disposed on a plane, the possibility of a leakage current flowing between the electrodes 63a, 63b due to dew condensation is low. However, the cost of manufacture of the leak sensing switch is increased because its production needs a manual process for the worker to insert the electrode pins 63a, 63b into the base 52.
It is an object of the present invention to provide a leak sensing switch which prevents a leakage current from flowing between electrodes due to dew condensation and manufacturing cost from increasing.
According to a first aspect of the present invention, there is provided a leak sensing switch formed on an insulating substrate. The leak sensing switch is formed on an insulating substrate and has a through hole defined in the insulating substrate and having a pair of inner side surfaces opposing each other across a predetermined space. A pair of conducting films are disposed respectively on the inner side surfaces. A pair of lands electrically connected to the conducting films, respectively are disposed on peripheral edges of the opening of the through hole in the insulating substrate. A pair of wiring patterns electrically connected to the pair of lands, respectively, are disposed on the insulating substrate.
According to a second aspect of the present invention, there is provided an insulating substrate having a leak sensing switch disposed thereon. The leak sensing switch is formed on an insulating substrate and has a through hole defined in the insulating substrate and having a pair of inner side surfaces opposing each other across a predetermined space. A pair of conducting films are formed respectively on the inner side surfaces. A pair of lands electrically connected to a pair of conducting films, respectively are disposed on peripheral edges of the opening of the through hole in the insulating substrate. A pair of wiring patters electrically connected to the pair of lands, respectively, are disposed on the insulating substrate.